The ultimate objective of this project is to determine if transovarial transmission of Japanese encephalitis (JE) virus and related mosquito-borne flaviviruses (St. Louis encephalitis (SLE), Murray Valley encephalitis, Rocio encephalitis) plays a role in the survival of these agents during winter or other periods adverse for their mosquito hosts. The more immediate objectives are 1) to elucidate the factors which affect transovarial and transtadial transmission of these viruses in both Culex and Aedes mosquitoes, and 2) to search for evidence of transovarial transmission of JE virus in the field. Experimental studies with JE virus will be carried out principally with the Nagasaki strain of Culex tritaeniorhynchus and Osaka strain of JE virus. Those with SLE virus will be carried out with a strain of Aedes epactius or Aedes atropalpus. Field studies to search for evidence of transovarial transmission of JE virus by Cx. tritaeniorhynhus and Culex annulus will be conducted at a site near Taipei, Taiwan. If it is demonstrated that JE and related viruses overwinter by transovarial transmission in mosquitoes, then a potentially new approach to disease control, or perhaps even eradication from limited areas, will be available. Control measures undertaken during the winter or spring against the mosquito species which carries the virus overwinter could have a more significant impact than a comparable effort directed toward the same or an other species which transmits the virus during the warmer parts of the year.